The complexity of communications systems has steadily increased during development processes. This is particularly true because the communication needs as well as the modes of communication of man have fundamentally changed as a consequence of new organizational structures and, consequently, new performance features and services must be implemented in the communication systems. For example, communication systems that are utilized for office communication have thus opened up possibilities for the connected subscribers in recent years to communicate with one another on different levels upon utilization of a multitude of performance features and services. The "VOICE" mode of communication existing up to then thus was expanded by performance features such as "REDIAL", "CALL REROUTING", "ABBREVIATED DIALING", etc., and new services such as "TELEFAX", "VIDEO TRANSMISSION", etc. have been introduced. Offering new performance features and services, however, usually requires an extensive and detailed interplay of the procedure residing in the respective communication systems. With an increasing degree of complexity for the procedures being executed, however, this interplay becomes more and more intractable. Problems thus arise in practice that make a faultless communication between two or more subscribers more difficult. High demands must thus be made of communication systems with respect to their faultless operation. The corresponding parameters have been defined world-wide by international standardization committees--for example, the CCITT--whereby special significance is accorded to the parameter of "probability of failure". These demands made of communication systems, however, thereby generally differ from those that are made of traditional data processing systems. Consequently, the interplay of the procedures of a communication system also occurs fundamentally differently than in a data processing system.
The procedures of the switching technology are accorded special significance insofar as they form the devices for the performance features and services. In order to be able to influence and control this interplay from the outside, data processing systems in the field of office communications are connected to the communication systems employed therein via appropriate connecting lines. Such communication systems employed for office communication purposes are already known from, among others, two articles in the publication "ISDN im Buero ", special edition of "Telcom Report" and Siemens-Magazin "COM" of Siemens AG, Berlin and Munich, 1985, (ISBN 3-8009-3846-4); "Hardware-Struktor des HICOM-Kommunikationscomputers", pages 58-66; "HICOM-SOFTWARE von Heute fuer Morgen", pages 67-75, and from German Published Applications DE 37 27 952 A1, DE 34 07 215 A1, all incorporated herein. Furthermore, systems wherein data processing systems are connectable to communication systems of the type set forth above are known from U.S. Pat. No. 5,007,080 as well as from the article by M. Doll "Computer Supported Telephony Application--Telekommunikation und DV im Duett", in NTZ, Vol. 43 (1990), No. 11, pages 820-824, both incorporated herein.
On the one hand, such data processing systems are used as storage systems for specific switching-oriented data of the communication system such as, for example, call charge data, subscriber data, etc. On the other hand, extensive procedures and processes that offer the user possibilities of intervening in the switching-oriented procedures of the communication system run on those data processing systems. It is particularly the presentations in the last-cited prior art that disclose a plurality of examples thereof. Thus, performance features and services can be linked both with one another as well as with external procedures, i.e. procedures running in those connected data processing systems, and can have their operational sequence automated. Such automated operational sequences are generally referred to as applications or functions. The programs that realize an application are deposited on the connected data processing system. The performance features that can be realized by the communication system are stored in the communication system itself and each have a respective external interface. As a result of their modular structure, the performance features can be selected and used by the applications of the data processing system via these interfaces. Thus, for example, the applications can access an electronic telephone book stored in the data processing system and can select the performance feature of "SELECT" in the communication system in accordance with their internal algorithm. Dependent on the respective result (for example, B-subscriber is busy), further subscribers deposited in the electronic telephone book can be selected in an alphabetical sequence upon utilization of this performance feature. The "TELEMARKETING" application or function represents an example of such automated operational sequences. TELEMARKETING represents an especially high-capacity function of marketing support for a customer consultant.
Thus, in the case of an intentional telephone contact by the customer consultant, the respective customers are selected according to a customer list deposited in the connected data processing system, and the telephone contact is set up between consultant and customer. Parallel thereto, specific, customer-associated data such as, for example, address, age, sales in the most recent fiscal year, etc. are displayed via a data display means at the work station of the customer consultant or service representative. When the terminal equipment of the customer, however, is busy, a renewed, automatic dialing by the system occurs at regular chronological intervals. The example of the "TELEMARKETING" function shows the interplay of the procedures of the data processing system with the switching-oriented procedures of the communication system. Information data as well as status data are thus bidirectionally exchanged via the trunks existing between the communication system and the data processing system. The data transmission usually occurs according to an acknowledgement method ("handshaking") universally known in the technology.
What are referred to as buffer memories are generally introduced in these systems, given data transmission problems. These are set forth in detail, for example, in the Enzyklopaedie Naturwissenschaft und Technik, Landsberg am Lech, 1980 Verlag Moderne Industrie, page 3469 (ISBN 3-478-41830-5) or P. R. Gerke, "Rechnergesteuerte Vermittlungssysteme", Berlin-Heidelberg-New York, 1972 (ISBN:3-540-05770-6), page 184, incorporated herein. What are thereby involved are memory systems for the chronological coordination of communication processes. A coordination is particularly required when data arise irregularly, and thus in an unpredictable time span. In this case, those data are collected in a buffer memory and are subsequently transmitted block-by-block via the respective trunk.
One example of irregularly arising data are status data, particularly status data of subscriber terminal equipment. An example of such status data is that the subscriber terminal equipment is a busy, free, initiation of a call request on the part of the subscriber terminal equipment. The status data provide information about the status or about status changes of the subscriber terminal equipment connected to a communication system, and thus arise irregularly in time and potentially in great numbers. For example, they are analyzed and evaluated by the "TELEMARKETING" function. For this purpose, they are transmitted via the trunk to the data processing system since the analysis and evaluation processes of the status data occur on the basis of procedures running thereat. Buffer memories are arranged at the ends of the trunk for the chronological coordination of the transmission processes. The status data arising in a chronologically irregular sequence are collected in the buffer memory and are subsequently transmitted block-by-block via the trunk.
In the prior art, the transmission processes are realized such that memory capacity in the buffer memory--in the form of sub-areas--is permanently allocated to the functions running in the data processing system--such as, for example, the "TELEMARKETING" function--, and the access of those functions to sub-areas of the buffer memory is thus enabled. What is problematical, however, is that those status data must be transmitted in extremely great numbers at times of high traffic load, and consequently the capacity of the sub-areas of the buffer memory is very rapidly exhausted. In this case, procedures of the dependability system must be provided that see to it that the trunk is immediately deactivated since, given overflow, only a part of the status data are transmitted, and thus an incomplete picture of the subscriber terminal equipment would arise in the data processing system. It also turns out that only some sub-areas have rapidly proceeded to their capacity limit in peak load times, whereas others still have adequate storage capacity available.
The abort of a connection is necessarily involved with a loss of all status data. As a consequence, this means that the procedures and functions running on the data processing system no longer have any information about statuses or status changes of the subscriber terminal equipment connected to the communication system.
The status data are usually transferred to an external storage medium so that they are available again at a later time via corresponding loading procedures. In the prior art, the buffer memory is usually dimensioned with a liberally dimensioned reserve in relationship to the arising data sets, an overflow being thus usually avoided. Narrow economical limits, however, are placed on such a liberally designed dimensioning. In practice, this means that even a buffer memory equipped with a reserve can no longer handle the data arising in peak load times and thus has its capacity exhausted--even though correspondingly slower than a buffer memory without reserve. Ultimately, a deactivation of the trunk can also not be avoided here. The outage of the trunk, of course, represents an undesirable limitation of the operating mode of the communication system in terms of its interplay with the data processing system.